How to Calculate Successive Discounts (20% Then 10%)
A shop offers 20% off, then an extra 10% at the till. Is that 30% off? No, and the difference matters when you compare offers.
Why they do not add
The second discount applies to the already reduced price, which is smaller, so it removes less money than 10% of the original.
The method
Final price = Original × (1 − d1) × (1 − d2)
Example
Original price 100. After 20% off: 100 × 0.80 = 80. After a further 10%: 80 × 0.90 = 72. Total saving is 28, so the combined discount is 28%, not 30%.
Combined discount in one step
Multiply the factors: 0.80 × 0.90 = 0.72. Then 1 − 0.72 = 0.28, or 28%.
Three discounts
10%, 10% and 5% give 0.90 × 0.90 × 0.95 = 0.7695, a combined discount of 23.05%.
Order does not matter
10% then 20% also gives 72. The result is the same whichever comes first, so you can compare stacked offers by multiplying their factors.
Comparing two offers
Shop A gives 30% off. Shop B gives 20% off plus 10% extra. Shop B ends up at 28% off, so Shop A is better by two points. On a 200 item that is 4 saved. Multiply the factors for every stacked offer before you decide, because coupons that look generous often combine into less than their sum.
Coupons often apply before or after other offers, and shops rarely explain which. Because order does not change the result, you can ignore that detail when comparing totals. What does matter is whether the coupon is a fixed amount or a percentage. A fixed 10 off a 40 item is 25%, but the same coupon on a 200 item is only 5%, so always convert it to a percentage first.
Try it yourself
Use our free percentage calculator to check your numbers instantly.